Method and apparatus for amplifying electric impulses.



R. A. FESSENDEN & L. COHEN. METHOD AND APPARATUS FOR AMPLIFYING ELECTRIC IMPULSES.

, PPLICATION FILED SEPT-2| I913.-

Patented Sept 5, 1916,

NOON.

NN W oo o u o n m E N NE 0 i N 0 n 0 UN 0 N Y. Q w 0 QN 0 S %wqww Q s M Q Q REGINALD AUBRY FESSENDEN, OF BROOKLINE, MASSACHUSETTS, AND LOUIS COHEN, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNORS, BY MESNE ASSIGNMENTS, TO SAMUEL M. KINTNER, OF PITTSBURGH, PENNSYLVANIA, AND HALSEY M. BARRETT, OF BLOOMFIELD, NEW JERSEY, RECEIVERS. 7

METHOD AND APPARATUS FOR AMPLIFYING ELECTRIC IMPULSES.

To all ziihom it may concern Be it lmown that we, REGINALD A. FES- SENDEN and LOUIS COHEN, citizens of the United States, residing, respectively, at

Brookline, in the State of Massachusetts, and Washington, in the District of Columbia,

have discovered or invented a certain new and useful Method and Apparatus for Am plifying' Electric Impulses, of which the following is a specificatlon.

' Our invention relates generally to the transmission of electric impulses and especiall to feeble impulses such as used n wire ess telegraphy and telephony; 1ts primary obje'ct being to magnify or amplify the received signals.

We have illustrated 'the invention in the accompanying drawing in which Figure 1 is a diagram illustrating c1rcuitsfor explanation of thephenomena we have discovered; Fig. 2 is a diagram showing the arrangement for use of our discovery in amplifying signals received by electromagnetlc waves. Figs. 3, 4: and 5, are similar diagrams showing difierent arrangements of apparatus for wireless signals as will be hereinafter explained.

It is already known that if an alternating current circuit comprises two parts which are closely contiguous parallel conductors, each one of which has an appreciable inductance, and a low resistance, then the current in each one of the said parallel branches may be larger than the'current in the main circuit. In fact, if the resistances of the two parallel conductors be small as compared with (L,-M)p and (L,M)p,

(L and L being the inductances of the par- 'allel conductors, M the mutual inductance and p the frequency multiplied by 2t:-- then the currents in the two parallel conductors will be opposite in phase, and the current in the main circuit equal to the difference between the currents in the two parallel conductors. (See FomuZw-ami Tables 05 Alternating Current for the Ualoalation Problems by Louis hen 143 to .14 1, and Recent Researches of Zectm'citg and Magnetism by J. J., Thomson (1893 edition), pages 512 to 515.) We have investigated a somewhat analogous phenomenon,

Specification of Letters retent. t t t, 5, 1 Application med September 2, 1913. Serial no. 787,630.

that is, the effect of a small voltage introduced in one of the parallel conductors, and being superposed on a large voltage operating in the main circuit; or vice versa, a small voltage being introduced in the main circuit and superposed on a large voltage acting in one of the branches of the parallel conductors. This is illustrated in Fig. 1 where 7 represents a high frequency alternator of extremely small voltage, 8 another high frequency alternator of considerable voltage, and 9, 10, in circuit are, two parallel conductors-of considerable inductance and very closely coupled so there is no magnetic leakage. Each branch circuit also includes an adjustable inductance 11, and capacity 12, for tuning purposes. Now in the case of a simple circuit, if we had one electromotive force acting, and introduced an additional electromotive force, the per cent. change in current produced would be motive force already acting, in a simple cir-" cuit, and then We lntroduced another electromotive force of say ten per cent. of the former one, the current in the circuit would merely be changed by ten percent. But in the case of this arrangement shown in Fig. 1, we have found conditions entirely different; for the'introduction of the additional small electromotive force due to source 7 will produce a much largerchange in the current of the two branches than corresponds to actual per cent. change in voltage. The same phenomenon results from interchanging sources 7 and ,8, but the constants of the coils 9, 10, will have to be different, and must be determined mathematically for every separate arrangement. In practice of wireless telegraphy, 1f the small current to be amplified is the effect of the voltage of incoming electromagnetic Waves of the signal, it is more convenient to have it operate on the main circuit corresponding to the alternator 7 shown in Fig. 1. These phenomena have been investigated mathematically and tested experimentally by us, and apparently they depend on the proper choice of the electrical constants of the two coils 9 and 10,

' tional to the square of the current, it is also clear that with this scheme we may detect signals of only one thirty-sixth the energy necessary to give a signal in a simple circuit.

For receiving, we may replace the source 7, in Fig. 1 by an antenna and thus utilize this arrangement for the amplification of the incomlng signals. Furthermore, for the detection of the signals we prefer to make use of beats-that 'is, we regulate the frequencies of alternation of the local source and the received waves, so that the difference in the frequencies will correspond to the frequency of an audible signal, say .1000 per second, which can be heard in an electrostatic heterodyne or electromagnetic heterodyne telephone as described in various Fessendens 7 dated January patents for example, 1,050,728, '14:, 1913. The arrangement is shown in Fig. 2, where 13 is the antenna, 14 a loading or tuning coil, 9 and the two branches of the parallel circuits, 15 coni densers, 16 a tuning coil, 17 a high frequency v alternator,'18 an electrostatic telephone, and a ground. The operation of this ar- 410- incoming wave acts on the antenna and imrangement' is similar to that of Fig. l: The

presses a voltage as did the generator 7 in are of difi'erent frequencies, loud beats will.

I Fig. 1, and this small added electromotive force Will produce a large change in the already existing current in receiver 18 due to alternator 17. Also, since the two currents be produced,the note being determined by the difierence between the frequencies of the so two sources of electromotive force.

I able manner so. as to keep the high frequency resistance low, and are wound to gether on. the same core and interlinked with each other so as to make the coupling very close and the mutual inductance hi h.

-We have 1n one case arranged the num er of turns on the two coils so that coil-10 is about thirty times the inductance of coil .9, and found mathematically and experime'n tally that for the other constants used in this particular instance this ratio gives about the best results; but of course other ratios of inductance will also give an amplification, though not to the same extent.

messes Moreover, the inductances of the two coils must always be adjusted with relation to the other constants, with a view to always keeping the mutual inductance high. This requires adjustment of each coil whenever the other'is changed. The exact relation between the inductances of the two'coils depends upon their resistances, the coupling that can be obtained and the frequency.

Although the arrangement shown in Fig. 2 is preferred by-us, various modifications may be used and obtain satisfactory results. In Fig. 3, for instance, the high frequency alternator 20, instead of being placed directly in one of the branch. circuits, is connected through a transformer 21, 22. In Fig. 4:, the alternator 20 and the receiver 18 are both coupled to the respective branches of the parallel circuits through transformers 21, 22, and 24c, 25, respect1vely. Another arrangement is shown in Fig. 5 in which we utilize the electromagnetic attraction between the two coils 26 and 27 for the detection of the signals in place of the electrostatic attraction shown in the other figures, 90 various other modifications may be obviously made, the essential method of amplifying being always in the employment of a main local current on which the received current is superposed in one of the branches.

While we have illustrated the use of our discovery in wireless telegraphy, it will be understood that its use may extend to many other forms of apparatus.

Having thus described our inventionand illustrated its use, what we claim as new is the following:

1. Apparatus for amplifying feeble alternating currents, comprising a main circuit traversed by said current and having branches including closely coupled conductors, means maintaining another alternating current in one of the branches of said circuit, and an indicator inthe other branch operated by the combined effects of said currents, said conductors being connectedto be opposed magnetically with respect to the additional current. 2. An ampl fier for wireless signals, comprising a receiver circuit having an indica-' The coils 9,: 10, are made up in any suit f its conductor closely ceiver circuit, the coupled portions of said tor therein, a shunt circuit having part of coupled with the re-.

' cuits.

. 3. The method of amplif ing signals in ;Wireless telegraphy by passing the received oscillations through a plural branched conductor, said branches havingparallel closely coil led portions of high mutual inductance an low resistance, and thereby inducing oscillations in said branches, and maintaining in said branches another alternating In testimony whereof we have hereunto y signed our names in the subscrlbed wltnesses.

REGINALD AUBRY FESSENDEN. LOUIS COHEN- Witnesses as to Fessenden:

EDWARD H. PALMER, SYRIA GPBITZ.

Witnesses as to Cohen:

P. S. AGNEW, ETHMA M. AGNEW.

presence of the two 

